[android] Fix gradle build for mopub dependency

Fix min sdk version

android/build.gradle

@@ -16,6 +16,10 @@ allprojects {
   repositories {
     mavenCentral()
     jcenter()
+    // TODO replace with google() for gradle 3.0.0+
+    maven {
+      url 'https://maven.google.com'
+    }
   }
 }
 
@@ -24,7 +28,7 @@ repositories {
     url 'https://maven.fabric.io/public'
   }
   maven {
-    url "https://s3.amazonaws.com/moat-sdk-builds"
+    url 'https://s3.amazonaws.com/moat-sdk-builds'
   }
 }